Speakers in bass and (especially) guitar amps are chosen for the color they impart to what is fed into them - very few of them are "transparent" or even close. Part of what it's really important in guitar is that distortion devices produce fizzy harmonics, and the speaker is usually called on to filter most of that out.
A well designed PA is intended to be a transparent system - it doesn't change the signal (or at least not too much). If you like the character of your signal when playing through an amp and cab, you probably want to emulate that in the signal you send to FOH. Now, the tough question: How much of that do you want to emulate?
Cab sims do two general things - they lop off some of the treble (the de-fizzing we spoke of before). They also lop off low end - the cabinets in your rig do not go low enough to reproduce the fundamentals of you lowest notes. When stressed, they will distort and make a bunch of garbage (why high passes come into the discussion so often here). BUT (and it's a big but)if you are playing through a really capable PA, that lost low end is not a bad part of your signal, it's a very good one. If you' replaying a 5, doubly so.
This is why I don't have a full cab sim in my chain - the PA's I get to play through have "big boy" subs (the kind that won't fit in your car, and that take multiple kilowatts a piece to drive them) A 5 played through them is glorious - if you don't filter off the low end. So, in my rig (which a is a pedalboard) I have eq that lops off some of the highs, but the high pass (yes there is one) is set at 17.5 Hz - it takes away infrasonic stuff, but leaves my fundamentals intact.
So, if you're playing though a PA that fits in your car or van, with subs that don't demand special power, you probably want to use a cab sim that lops off both high and low frequencies. If, however, you're pulling into a venue that has a big PA installed, or you've got a couple semis for you band's gear, then you probably want a cab sim that just lops off the highs. For bass, either can be done well with a parametric eq (a Source Audio EQ2 is great for this) - you don't need a digital IR based cab sim to get the functionality you need.