Ok... Here's a few things.
When you're on L0 - and your computer goes into deco. Those are mandatory deco stops. It won't say "level stop" it will say "deco stop" - the dive time remaining during your dive on the display that says "no stop time" is counting down to deco. It will start you with 1 minute of Deco at 10' - this means you're having to do mandatory safety stops, since the UWATEC only goes from no stop diving to - diving with stops.
When you're in L1 - L5... your "no stop time" is counting down to your first level stop. At 10'... When you're in L1, you will have more "NDL" (although it's not really NDL, it's a level stop, not a deco stop - and your not really diving to the NDL on any table) time than in L5. There is a chart in the instruction manual illustrating this, and you can download the manual from UWATEC.
If you're in L1 - 5 the level stops are OPTIONAL. Meaning, if you blow off a level stop, the computer will ONLY penalize you by moving you to the next lower L group. Like if you're in L5 (most conservative mode) and it gives you 2 minutes at 20' and then 3 minutes at 10', and you blow the 20' stop, and go right to 10'... the computer will move you from L5 to L4.
If you're in L1-5 and the computer says "DECO STOP" or at any time the display says "DECO STOP" this is a mandatory deco stop, and if you blow that off, it will lock you out for a while, and you probably shouldn't dive for the rest of the day.
I dive a few times a week, like more than 100 dives in 2006... I leave my SmartCom computer on L1. Even L0 is fairly conservative, with respect to the tables, since remember - the computer is counting NO STOP DIVING, so that is the area on the tables before "mandatory safety stop" (the part in grey on the PADI table) is in play
It is always advisable to do a safety stop, and count your 3 minute safety stop on a watch, or just count off 3 minutes on your UWATEC computer.
If you're only diving a few days out of a week on a vacation, and only doing 2 - 4 dives a day, I would tell you that setting your computer to L3 is a little extreme, and would limit your diving to a rediculously conservative amount of time. You can easily check the dive planner mode on the computer to see what kind of time it's going to give you at a certain depth, and compare that to the dive tables.
I hope this makes sense...