You have to remember that an ESD discharge into a component may not render a device useless, but can cause 'pits' in the silicon and can cause the device to prematurely fail. If you are a hobbyist and are willing to take the risk of ESD damage than it is your choice, but in the professional field you don't want to do that. It is a good way to have warranty issues and it isn't a good practice at all. You want to minimize damage as much as possible. ESD discharging can also cause intermittent failures on devices, especially microprocessors that have billions of transistors. Just because a device was hit by ESD doesn't mean it won't function at all, it means that the part is no longer reliable and should not be used in a unit that you plan on using in a production atmosphere. One example of a device is an amplifier. Op amps can get very expensive depending on your power demands, bandwidth, common mode rejection, and distortion ratings. ESD damage can cause an expensive amplifier to inject unwanted noise into a signal and cause distortion (in audio) or power loss (on power units).
If you are going to be working on more expensive items, such as computers, which deal with microprocessors, or DSP (digital signal processors), then I suggest you take the hit and get an ESD mat. I know they are expensive, but the last thing you want to do is cause damage to a $100.00 or $250.00 device. You will thank yourself, and so will your pocket book.