changed default: compression=None in write

anndata/base.py

@@ -1917,15 +1917,16 @@ def _check_dimensions(self, key=None):
     def write_h5ad(
         self,
         filename: Optional[PathLike] = None,
-        compression: Optional[str] = 'gzip',
+        compression: Optional[str] = None,
         compression_opts: Union[int, Any] = None,
         force_dense: Optional[bool] = None
     ):
         """Write `.h5ad`-formatted hdf5 file.
 
         .. note::
            
-            Setting compression to `None` can dramatically speed up writing.
+            Setting compression to `'gzip'` can save disk space but will slow
+            down writing and subsequent reading.
 
         Parameters
         ----------
@@ -1945,12 +1946,12 @@ def write_h5ad(
             raise ValueError('Provide a filename!')
         if filename is None:
             filename = self.filename
-
         if force_dense is None:
             force_dense = True if self.isbacked else False
 
-        _write_h5ad(filename, self, compression=compression, compression_opts=compression_opts,
-                                                             force_dense=force_dense)
+        _write_h5ad(filename, self, compression=compression,
+                    compression_opts=compression_opts, force_dense=force_dense)
+
         if self.isbacked:
             self.file.close()