I would point out the 2d6 for hp for goblins...I know 4 DMs as well as myself (sorry we dont all know each other 4 is what I have) and through the streams I watch and DMs on youtube and all that...I have never seen anyone roll for creatures. It would be such a pain in the ass. You might have 6 goblins with 2 hp. The variability of the encounter then makes you say "well thats too weak, lets just keep adding them until its challenging" because youre a DM and you know how numbers work and you know what your PCs are so you have a prettty dialed in understanding of what it will take. It would also make you decide if you want pack tactics or individual initiative depending on the HP and number of gobbos and you run the risk of a band of 12 goblins TPKing on a good initiative because of damage output instead of just 5 being a reasonable fight that has a more controlled swing.
If it says 2d6 its 7. Hobgoblin is 2d8+2 thats 11. You do the average, then round the hit dice (down), then halve that number and add it to the average. Young Red dragon? 17D10+85. Which is 17*5+85 = 170. 17 rounded is 16/2 8 = 178. If a DM adjusts bosses and stuff like that, fine. Your rank and file is gonna be straight out of the book though, so I wouldn't use hit die rolling as a factor, it just doesn't happen unless the DM has said ALL goblins in this encounter have 10 instead of 7. No one manages that crap by hand, its prohibitively time consuming to run and track the minis to their sheets.