A good reason for including financing information in your home purchase offer is to protect yourself. If interest rates suddenly become volatile and start to rise quickly as sometimes happens, you may be looking at a mortgage payment much higher than you had anticipated. By putting a maximum acceptable interest rate in the offer, you are protecting yourself from such an occurrence.
At the same time, the seller will probably want to see that you have some flexibility in the financing terms that you are willing to accept. If interest rates are currently at 5% and you indicate that this is the highest rate you will accept, you would be able to cancel the contract without penalty if interest rates rose past that percentage point. The seller would suffer because they have lost valuable marketing time and may have made their own plans based on successfully closing the transaction.