You'd be surprised how many vendors ship applications without a single index, much less properly aligned clustered indexes.
Heaps are bad. You can't defragment a heap by performing index maintenance, despite old myths about the create/drop a clustered index trick.
Similarly, the myth of a heap performing better on pure inserts vs a table with a clustered index is an academic one. Heaps are impossible to order, which means selecting from a heap is always a scan.
If your table will be constantly written to and rarely read, put a clustered index on it. The writes will be sequential, resulting in
EDIT: Page "breaks" (I meant splits) aren't possible on heaps, but forwarding pointers, which create a maze of bad performance in heaps with nonclustered indexes. Thanks to commenters for pointing this out!
And when you have to look in that table for a stray logging record, it won't be a full table scan. If your table will be constantly written to and never read, why is it in your database? Such a table doesn't exist.
This script is an easy one to use for finding heaps in a database, along with the row count and size of jumbled data that is haunting your database. It is in my DBA toolbox folder alongside many other scripts.
--Doesn't work on 2000 databases or databases in 2000 compatability mode. Need to change the db_id() syntax if so. select [Database Name] = db_name() , [Table Name] = s.name + '.' + o.name , p.row_count , SizeMb= (p.reserved_page_count*8.)/1024. from sys.objects o inner join sys.schemas s on o.schema_id = s.schema_id inner join sys.dm_db_partition_stats p on p.object_id = o.object_id inner join sys.indexes si on si.object_id = o.object_ID WHERE si.type_desc = 'Heap' and is_ms_shipped = 0 order by SizeMb desc
As an aside, but a different blog post altogether - a good clustered key is narrow, unique, unchanging and sequential - which is why IDENTITY integer columns are the perfect clustered key. Compound clustered keys can be a big waste of space.