Personally I haven't done it much but I'm doing a German/French accent for a Minotaur Druid so that'll be fun.

As DM? Sure. It provides variety and recognition for the various NPCs, as well as setting tone and atmosphere.

As a player? Nope. It just becomes burdensome after a while and I end up forgetting to bother. It doesn't add much to a PC in my opinion because, having a 1:1 relationship with the portrayer, identification isn't an issue and there is plenty of characterisation throughout the adventure for the character without it..I'll add emotional intonation and, if the accent is particularly relevant (eg my squeaky Gnome got angry the other night, so I put the accent on for the comedic effect), I might add it, but it's generally ignored. Too much hassle for too little gain.

I'm in the sometimes camp, I'll often shift in and out of tailored voices for characters depending on the game and if we're doing something that is RP heavy or not. I'm not massively keen on doing accents, instead I mostly focus on shifting tone and pace or using alternate speech patterns for characters. When I'm DMing, even though I'm mostly behind a computer screen with no camera, I'll also act out certain movements and activities that my NPCs are doing to help me maintain the personality.

As a player, I will, at a minimum, adjust my cadence, tone, and diction to match the character—even if not always speaking in a fully different accent.  By utilising a different voice than my own, it not only plays into the roleplay element, it makes it easy for other players to distinguish when I am speaking as a player and when I am speaking as a character. 

As a DM, I frequently subject my players to my terrible accent skills, often with exaggerated effect.  Wildly different accents on NPCs within the same conversation help the players keep track of who is who, and ensure everyone knows what dialogue is ascribed to what NPC.

I do as a DM because I have so many NPCs to differentiate. I don’t always do it as a player, although sometimes I do.

I try to, but often become burdened with self consciousness and revert to my own voice, both as a DM and as a player.

I am working on improving my ability to keep track of various NPC's and their voices!

Always. Some of them aren't very good... sometimes when I'm DM'ing I forget what voice I used for a character if they haven't been around for a while, but I always speak differently as a character than my normal speaking voice.

I'll often try; though it's slightly more a change in diction and speech pattern than a "voice" so to speak.  For example: my necromancer wizard is an academic: so he's normally calm, collected, and rather verbose.  My eldritch knight fighter by contrast is quite blunt and to the point.  My stealthy horizon walker ranger is generally quite soft spoken, slightly formal, and generally conservative with his words; not in the "edgy guy who doesn't talk to anyone" sort of a way, more "only speaks when necessary" sort of way.

As a player, yes. For me it helps to easily tell when I am speaking in character, to other characters, or as a player to other players/DM.

I'm definitely not good at it! And most of my voices are a sort of vague Irish/Welsh/Nordic something. But it's fun!

A friend of one of my players found out I DM and asked me to run Mines of Phandelver for him and his group.  I was more than happy to but after one session heard they were ripping on me because I didn't do voices for NPCs and monster sound effects, etc.  

I am self conscious as well when it comes to voices and theatrics and even more so in front of a rough crowd so I backed out of further games for this new group.  

I can't do voices in my own language. I can do all sorts of things in english - but danish just doesn't work for me. Unsurprisingly, I mostly play with danes, except for pbp, which is always in english, but doesn't really require much in terms of voice acting =)

I like to do voices as a GM, although not for every character and not every time. I use pitch, vocabulary, and mannerisms to differentiate my NPCs.

I try, but it doesn't seem to be part of my skillset just yet. Hoping that will change with time and experience.