Running a Debian installation on Android as a NAS / VPN - what would I lose as compared to a Raspberry Pi or similar comp? I have a rooted Android phone that is no longer in use.  I have currently been using Linux Deploy on an Android tablet to run a Debian installation in chroot, and have found it so useful that this (very cheap low end) Android tablet has replaced a laptop.  From this experience I am wondering if I could use a similar installation on the old phone as a NAS / VPN at home.  For some reason, the Debian install running on the tablet does not seem to be stopped / offloaded by the Android OS - i.e. I can SSH in at any time, even 10 hours after use, and it still responds. 

I could of course purchase a Raspberry Pi or similar device.  However, I live in a smaller city in India, which means this proposal has two disadvantages - 1) unlike a phone, the Pi has no protection against the frequent one or two hour power cuts that take place here (a UPS would not last long enough) and 2) the cost of a Raspberry Pi in Indian rupees is not expensive, but high enough that it's not something I can simply spend on without thinking.  

So, what would be the disadvantages of using an Android phone as, effectively, an ARM-based Linux computer?  

I am aware of this question but neither the question nor the answer seems specific enough for this purpose. 

NB: By a NAS I don't mean a device to which I could attach external storage - the storage in a microSD card in the phone should be plenty.
Disadvantages

I'm assuming that you already know the advantages, so I'll just tell you the disadvantages:

 Hardware errors: Many users have reported this. Issues include (but aren't limited to) WiFi connection errors, Bluetooth not working, Hardware buttons not working, etc. (These obviously vary from phone to phone)

 OS errors: Some users have reported that Linux hangs randomly and that the phone needs to be forcefully shut down by long-pressing the power button or taking the battery out. (These depend on which distro you are using)

Software errors: A friend of mine says that some software doesn't work the same way it would on a PC. You have been warned :/

Driver errors: Some hardware may not be detected by linux. This depends on the distro you are using and the hardware support provided by it.

Hardware Comparison

Here's a comparison:

-------------------------------------------------------------------------
|Criterion              |Android (Android One)  |RaspberryPi            |
|-----------------------|-----------------------|-----------------------|
|Connectivity           |                       |                       |
| (a)Bluetooth          |Built-in               |External Dongle        |
| (b)WiFi               |Built-in               |External Dongle        |
| (c)SIM - 2G           |Built-in               |External Dongle        |
| (d)SIM - 3G           |Built-in               |External Dongle        |
|-----------------------|-----------------------|-----------------------|
|Specs                  |                       |                       |
| (a)RAM                |1-2 GB                 |1-2 GB                 |
| (b)CPU                |1.3 GHz                |1.2 GHz                |
| (c)Storage            |SD card + internal     |SD card                |
| (d)SIM Slots          |2                      |None                   |
|-----------------------|-----------------------|-----------------------|
|Battery                |Internal               |External               |
|                       |(Fixed Capacity)       |(Your Choice!)         |
|                       |(Use Power Bank)       |                       |
|-----------------------|-----------------------|-----------------------|
|Cost                   |INR 6999-8999          |INR 1299-3899          |
|                       |USD 100-150            |USD 20-60              |
|                       |                       |(+Extras)              |
|-----------------------|-----------------------|-----------------------|


Conclusion

So what does all that (^) even mean? According to me, it's worth a try. If it works, congratulations, you are a very lucky man (or woman). If it doesn't, take it as an interesting experience...

TL;DR: Try it, but don't expect too much...

PS: 
The are plenty of ways in which this can go wrong [see https://github.com/meefik/linuxdeploy/issues ]

A tutorial and some troubleshooting tips can be found at http://null-byte.wonderhowto.com/how-to/rooted-android-your-new-pentesting-tool-0159093/