Depending on exactly WHAT repairs are needed...
I have seen many owners buy a property in marginal condition, then do "just enough" to get by and rent it out so they get the cash flow started. So, you move in a tenant that's not too picky about the condition. He's probably not picky because that's the way he left his last place...his family is just hard on things. Of course,since the unit isn't "sharp", you have to rent for well below the top of the market, in other words you are giving up cash. And then the service calls start coming. You send a plumber...oops, $150. Then an electrician...oops, $300. Then a closet door "just fell off", and you spend another $125 rehanging and repainting it. A few months slip by, and its time for a renewal. You actually take the time to look INSIDE the unit...and discover amazing "artwork" about 4 feet up the wall....EVERY wall! Well, the kids sure liked it... and there's the rusted through trap with an overflowing bucket under it. They never reported a problem with the drain, and now you have a sink base cabinet delaminating, mold, and more repair bills.
Yes, some of this you can bill the tenant for, and maybe even collect it, eventually. In the meantime, YOU get the aggravation, the 6 PM Friday calls, etc. etc. Repairs and maintenance done piecemeal (and often at "afterhours" overtime rates), and especially low quality repairs that you end up Re-doing in a year, will break you.
Or, you take into consideration that when it was new, the property had a design life of 40-50 years, and now, most of that life is used up. So you renovate...STARTING with the mechanical systems...plumbing, electrical, HVAC. (Today's tenants need LOTS of grounded outlets, and many expect air conditioning or at least nice ceiling fans) Update your cabinets (or faces) and fixtures, the tub and surround (at a minimum reglaze), some paint and floorcovering, and now YOU can expect 20+ years of pretty trouble free service. You have a modern looking, attractive and fully functional unit that interests the more discriminating tenants...the ones that actually take care of their home. They actually appreciate that you have provided a nice home, and they pay top rents, on time. Service calls are virtually eliminated for the next ten years. Life is Good.
Over the next 10-15 years your cash flow will be better than the marginal property, and you will have much less aggravation. As an added bonus, in all likelyhood the value of your property has appreciated
OTOH, if the basic structure is ALSO in poor condition, AND the roof is bad, and its not that great of a location, or floorplan, or... then it won't make any difference- you're looking at a teardown.
It also probably won't work if you are unable or unwilling to do any of the work yourself; and/or if you are picking all new contractors out of the Yellow Pages.
In general, I disagree with the idea of doing just enough to get it rented, then make it nice when its time to sell. Why give someone else the benefit? Make it "new" for you, get the best tenants, the highest rents, have the least headaches, and enjoy life!