The only good reason to go is to stake out the position that the siege needs to stop. This is not what our news outlets are reporting, however.
What Blinken has been thrashing out over there is humanitarian plans to be implemented prior to the invasion that appears to be a foregone conclusion. Israel wants food, water and medicine going in through Rafah, but is balking at fuel due to concerns that it will end up in the hands of Hamas. I would imagine that Biden is also there to secure getting Americans out, though the Egyptians are refusing until aid starts flowing.
The whole thing will require cooperation, and both Egypt and Saudi Arabia have been yanking Blinken's chain. Egyptian rhetoric has not been kind (go figure), and Saudi's crown prince made Blinken wait for hours. It's not clear that all the parties will get over the line, though the urgency of the situation may put some objections on both sides to bed.
I don't think tying himself tacitly to an invasion of Gaza is a good move by Biden, but he likes face-to-face and it's hard to tell a president "No" in the best of times.