In my country (Western Europe) it can be an issue, because if you are considered too insane to be held accountable, you'll go to the clinic until you are not a danger anymore. Whereas sane murder can get you up to 30 years (or life - which really means prison for the rest of your life - although I don't think that penalty is ever given anymore), with an average of just under 15 years, an insanity clinic 'sentence' can potentially last for the rest of your life.
A result is that some criminals refuse to comply with a court-ordered psychiatric evaluation (the court can force you to turn up, but they can't make you talk to the doctor), because they prefer the definite prison sentence. Especially if it isn't expected to be a very long sentence.

They try to make the intramural part of the clinic stay less than 6 years - if you are fit to leave after 1 year, you'll leave after 1, and if you are fit to leave after 8, you'll spend the last 2 years in the longstay. Also, the intramural part isn't usually administered if you commit a crime which has a maximum sentence of less than 6 years (there are exceptions, stalking is one) no matter if you were insane. You might have forced outpatient treatment, therapy, medication, a stay in a normal or normal forensic clinic (basically the forensic ward of a mental hospital, but those stays are usually much shorter and it's less prison-like) though. Or restrictions (no drinking, curfew, whatever necessary) or moving to a halfway house.

Or maybe indefinite intramural time can't be given after a less-than-6-years sentence.. just definite, short-term. Not sure, I am no lawyer.

Basically - prison is to punish, and insanity clinics are to lap you up until you are not significantly more likely to commit a crime than the average person. And that can take longer than the maximum sentence for your crime, and if they can't fix you to that point, there is a possibility of you never leaving.