It's fine to let another person use part of your land temporarily. For example, maybe a neighbor would like to extend their vegetable garden onto a bit of your land that is currently mostly weeds. However, it's important to create and sign a rental agreement between, so as to prevent that person from eventually claiming ownership by a legal doctrine known as "adverse possession."
Even if the neighbor didn't talk to you in advance; for example planted the vegetable garden over your property line then built a fence to encloses it; signing such an agreement can be legally useful, particularly if you'd rather live with the missing piece of land than fight over having the fence removed). Also, you can earn a bit of cash this way, though keeping the rental amount minimal will make it easier to get the neighbor to sign.
For someone to acquire title to land through adverse possession, their use of the land must be "hostile," which essentially means "without permission." A lease or rental agreement, of course, constitutes documented permission by the owner to the possessor, and would thus defeat any future claim that the individual "owns" your land. Read more about this strategy in, Avoiding Adverse Possession Claims by Renting Portion of Your Property to Neighbor.
While you should certainly work with an attorney to draft the lease appropriate for your situation, a sample lease with some of the key terms to consider including is below: