The main disadvantage to traveling alone while on safari is cost. The per-person rate of a room or tent will invariably work out much more expensive if there's only one occupant. The same principle applies to the cost of charter flights and car hire; if you're looking to spread costs a little, it's a good idea to partner up for your trip. Ranger Safaris (www.rangersafaris.com), the biggest operator in Tanzania, deals with big catalog operators but also offers a large selection of scheduled small-group "seat in vehicle" itineraries, making this a good value option for singles.
Of course, if you're planning a totally budget-oriented adventure where you'll be jumping on buses, making use of relatively inexpensive tour operators, and shacking up in cheap local places, you can have a perfectly good time on your own, with great flexibility to do what you want, when you want. There is some price to pay for such independence, though, such as never having someone to watch your bags at airports and the like, or keep an eye on your drink if you need to visit the washroom. Hopefully, if you're planning to explore on your own, you'll be sufficiently outgoing and gregarious to make friends and acquaintances along the way. The other alternative is to join an overland truck safari, which can be ideal for single travelers. For details of routes through East Africa, visit www.overlandafrica.com.