It can be the thing that gets you into a home. It is also a much larger commitment for them than most families realise when they agree.
A co-signer is not a character reference. They are equally responsible for the entire mortgage. If a payment is missed, it affects their credit. If the mortgage defaults, the lender can pursue them for the full balance, regardless of who was living in the home or who agreed to pay what between you.
Frequently they also go on title, which brings its own consequences.
It affects their own borrowing capacity. Your mortgage appears as their liability. A parent who co-signs may find they cannot refinance, buy a rental, or help another child later, because on paper they already carry a substantial debt.
If they are on title, there can also be tax implications when the property is sold, because it may not be their principal residence. That is a question for their accountant, and it should be asked before signing rather than years afterward.
The conversation worth having out loud: what happens if you lose your job, if you separate, if you want to sell, or if they need their borrowing capacity back. Families that discuss those four scenarios before signing rarely have problems. Families that assume it will be fine sometimes do.
This is the part to plan at the start. Removing a co-signer generally requires refinancing — you re-qualify on your own, and if approved the mortgage is rewritten without them. That means it depends on your income and the rules at that future date, neither of which you control today.
Set an intention and a rough timeline when you sign, and revisit it at each renewal. Co-signing arrangements that were meant to last two years and quietly ran ten are common, and they are the ones that cause friction.