why does everyone spend a night at horseshoe instead of at whitney portal? Crowds? Cost? Noise? Extra 2K vertical?
A little bit of each. The extra 1.7k is nice, but it really comes down to logistics, timing & convenience.
Day Hike Assuming you even had a legitimate site at the Portal car campground the night before the evening of your actual hike, what would you do all day long once you were checked out? (Note that you typically have to check out of official FS campsites by noon.) You could move your car to either the day use or even overnight parking lots, but then what? You can't hike past Lone Pine lake without a permit, and while Meysan is a nice hike, you could seriously tire yourself out beforehand.
If you spend the night @ Horseshoe, however, there are myriad trails radiating out from the various parking lots that don't require a day use permit. They are also practically flat eg a 10k->11k elevation gain over 5 miles to the first lakes. So, you spend the night, cruise around a little bit to get some exercise in the morning, then mosey on back down to LP in the afternoon. Maybe go to dinner, etc, then eventually head up to the overnight backpacker site (or the back seat of your car) @ the Portal.
Whether it's noisy, crowded or not, you're still not going to get any sleep. Waking every hour, checking your watch, then finally about an hour before your planned departure, you'll say the heck with it and just get up. Everyone else will be doing the same, so even if you're a really sound sleeper, your fellow aspirants will provide the alarm.
Overnight The Portal campground can work if you're hiking to Outpost, etc, for another day of acclimatization, but then another problem arises: it's a popular campground that is often reserved far in advance for multiple days. So, in other words, good luck getting a site. Horseshoe on the other hand is a huge area with multiple, large parking lots. So, while it may technically have fewer 'official' camping spots, it's under patrolled and pretty easy breezy as long as there aren't any problems.
So, you crash there without any hassles, head over to the Portal in the morning, and begin your hike to your base camp.
