It all depends on the height of the grass you start mowing and how much you want to remove. For lawns, the usual recommendation from horticulturalists is to cut no more than one third of the length. So if the length is 4.5 inches, you clip off 1.5 inches leaving 3 inches. Most people would not bother collecting this small amount. Some might choose to use a mulching mower, but normally just cutting off the top third with a side discharge mower produces excellent results. However, if there is a delay in getting the grass cut due to rainy weather or other conditions and it grows to 6 inches or so in length, then a side discharge mower will definitely leave windrows. The manufacturers of mulching mowers generally say in their Operators Manuals that mulching mowers do not perform well in wet or tall grass, and I have found that to be the case. So I do not try to mulch if the grass is already too long. If it is too long, I typically mow once with a regular mower, and then go back and mow again in a different direction. Usually this disperses the windrows and leaves a reasonable finished look at least until I can get back on track of mowing regularly. If it is too long even for than I use a lawn vacuum. So, in general, rear discharge and mulching mowers work best on turf that can be kept mowed regularly with minimal length cut off. Mowing on golf courses is often done several times a week to maintain the high quality of appearance and grass length desired by golfers. Usually several different types of mowers are used depending on the grass length and the length of cut required.
I assume in your reference to mowing paddocks or pastures the grass would not be mowed nearly as often as a home lawn. Neither a mulching mower nor lawn vac would work well in tall grass. A side discharge mower can still work here if the grass is say 8-10 inches tall, but there will be windrows produced. Anything longer requires a deck designed to handle it. I use the Ventrac Tough Cut deck for tall materials. I maintain trails in a wetland preserve with it and it works very well. It is not suitable for maintaining a lawn around a home.
My bottom line is that you may need more than one type of deck to handle your 2 different types of mowing. However, if you have only one deck, then a side discharge style is the best compromise.
JackIL