Wallets are the main access point for users to manage, send, and receive their coins. Compiling a wallet, however is not something that every user knows how to do, and the learning curve for entry into proper compiling can be too much for some to handle. When your user base can be comprised of multiple OS distributions and flavors, there is nothing more frustrating for a user than to find out that a coin they are interested in doesn't offer an easy way for them to manage their coins from their own computer.
Give your users and supporters the option to jump right in with pre-compiled wallets for a variety of OS distributions!
Having a wallet available for users just isn't enough to maintain your coin's network, many users computers are behind consumer firewalls that may or may not allow for the automatic port forwarding necessary for OTHER wallets on the network to establish a connection. Having a stable and dedicated set of nodes that can connect freely to each other and allow incoming connections is vital for any coin's network to survive. As a coin grows in use, existing static nodes may reach their limit of incoming connections or become bogged down trying to process the connections they can establish.
Adding more nodes to your network can relieve some strain on existing nodes and provides more capacity to your network.
Making wallets aware of nodes on the network is pretty important! Many methods have been used to facilitate this over the years: hand-coding IP addresses (or hex strings) right into the wallet's source code, using IRC channels behind the scene, or even distributing long lists of "addnode" lines for users to dump into a conf file. Each method has it's merrits, but also it's shortcomings; from extra wallet releases, to security risks.
DNS Seeders constantly crawl your network and return always-updated lists of REACHABLE nodes that wallets can use to establish initial connections.
Block explorers offer up a multitude of additional analysis options for tracking transactions, block times, address balances, and more. Powered by the blockchain itself, a block explorer makes the entire history of every block and transaction available at moment's notice to anyone with a modern web browser. More recent wallets can even link directly to a block explorer to show transaction details not normally available in the wallet's UI display.
Having a block explorer for your coin is also a requirement for listing/addition on some exchanges or payment gateways.