Great answer, the best explanation I've seen,,,It depends.
For conventional, the scanner will complete its "scanning loop" (going from the first frequency to the last frequency) faster because there are less frequencies to check for activity. With conventional, the scanner checks all the unavoided frequencies for activity, one at a time.
With trunked, the scanning process is much different. The scanner listens for an active control channel frequency, one site at a time, spending about 2 seconds (give or take), listening for "channel grants". A channel grant is approval to transmit and assignment of all radios on a talkgroup to a voice channel/frequency. Your scanner will see if the talkgroup is in your list of talkgroups you want to hear. If so, the scanner will tune to that assigned voice channel/frequency. The scanner is NOT listening to each talkgroup, unlike in conventional scanning. As such, the number of talkgroups will not impact how fast the scanner does "its thing".
Where Avoids come in to play with scanners, is when sites are avoided. So if you limit the number of sites (assuming you are monitoring a system covering a large area such as the Indiana trunked system, yes scanning is hastened. If you are trying to monitor the Gary Indiana site while you are in Indianapolis, you are too far away, however, the scanner will still "listen" for possible control channel activity. Since its too far away, time (milli-seconds) will be wasted. (No reason to spend scanning time hearing something you can't at a cost of missing something you can).
If you do an avoid it can never scan slower. Only faster or the same as if it was not avoided. Ideally the firmware would be written so that it checks if an avoid are done before it loads the frequency to the receiver, then it will scan faster with each avoid. If the firmware are not so effecient coded then it could load the frequency to the receiver and waits for the frequency syntheziser to settle and if squelch are detected it starts to test if the programming are done with CTCSS or it should be a digital decode or if it's avoided. Then the scan rate will be unaffected, neither slower or faster. This is for conventional frequencies.I have avoids in my favorites. Do they cause a longer scanning time? Should I just take them out?