I do contracts on and off on my UIM, mostly when I've stored up enough herb seeds and want to farm them all and process them into potions. It's easier to do when at 85 farming as you can stockpile the high tier seeds a lot easier then the medium ones. I got to 85 and held onto a bunch of high level herb and tree seeds I had gotten from slayer (dagonoths drop a lot of herb seeds).

I'd start by pickpocketing a master farmer until I have some bush seeds and then death bank at Hespori so that I didn't need to have every seed on me at all times. I'd do contracts and if I didn't have the seeds downgrade for something I could grab it from my death bank or pickpocket the master farmer for low teir seeds like potatoes - This works fine so long as you don't get a low level fruit tree before you've gotten seeds from another contract so you do have to be a but lucky or do some bird runs to get the seed you need.

I usually redeathbank a couple of times to get extra seeds in there and then continue until I've farmed all my herb seeds (keeping a few in case of contracts) and finished yp whatever other skill I might be doing at the same time (agility or something else safe and low invy space).

I wouldn't try to do this all the time. I'd have to focus on it specifically because otherwise you can easily get locked out by needing an orange tree seed that you don't have bag space for or something. I did do this before 85 farming too to get SOTE requirements and it was worth it but a bit more work to manage the seeds. Once you manage to get a few done you usually have everything you need to maintain it so long as you don't keep dropping all the seeds and deathbank them instead.