Has this been a big issue in your games?
Yes. When I started my game, I allowed constant switching of characters until we hit 3rd level (which took 6 sessions). So if they wanted to try a new character concept every game, that was fine. However, at 3rd I wanted them to pick something and try to make that character survive. They did not. Instead, they ran headlong into overwhelming odds, died, and spent hours mid-game rolling up new characters. Then they got greedy and started killing each other just for the loot. (New characters using the wealth guide in the DMG come into the game with a few gps more than the existing characters, so they had $$$ in their eyes).
So eventually I had to use what I call the Raise Dead rule. That is, if a character dies usually the Raise Dead spell brings that character back, and in so doing, the character loses a level. That's just a limitation of the spell, right? So my rule is that if you die and DON'T want to be brought back to life, then your new character
still has to lose a level. And that's relative to your own character, not the party. So if one person dies a lot, that person will end up really low level.
So I have one kid who died and fell back to 3rd level for his new character, and then died again and had to create a 2nd-level character, and then as we introduced that character into the game -- before ANYTHING had happened -- he wanted to toss that character sheet and create a new character. So I said, "OK, but it has to be a level lower than the current one, so that means you'll play a first-level character in a party of 4th level characters. If you die, you'll have to play a 0-level commoner."
Hearing that he might end up playing a 0-level commoner is the
only thing that has abated his indecisiveness about what to play.
In addition, I've started introducing alignment shifts and XP penalties for intra-party assassination. Without it, some of my players would have "lawful good" paladins that behave chaotic evil, and they wouldn't have a problem with it.