Always size before loading. I have seen new brass be a little egg shaped.
Trimming? Some swear they never do it or have never needed.
If you are loading for accurate, or long range shooting, or especially competition,, Then by all means check everything. By not trimming then the OAL will be different. Differences is not necessary. Take the time to check everything. Same with the bullet seating. Everything needs to be the same for the most accurate loads. Differences in bullet seating will cause vertical stringing.
Read s4s4u little motto: short cuts often lead to long recoveries.
If you are in that big of a hurry then just go buy some factory loads.
Nickel brass especially should be sized before loading (the first time even)!! With nickel they can be oversized just enough, that the finished cartridge will not seat completely in a tight chamber. And some of the S&Ws such as my 27 will not take loads that have not been properly addressed.
45MAN is right. Nickel has a higher COF than brass.
oh,,, COF ( coefficient of Friction ) Lower is better. Nickel needs help.